Anatomy Atlas

Lumbar vertebrae

Vertebrae lumbales
Also: L-spine · Pars interarticularis
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Five large weight-bearing vertebrae of the lower back. Spondylolysis, spondylolisthesis and lumbar spinal stenosis are their key clinical problems.

Core anatomy

Location

Lower back, L1–L5, between T12 and the sacrum.

Classification

Irregular bones.

Key features & landmarks
  • Large, kidney-shaped bodies (the heaviest load)
  • Short, thick, hatchet-shaped spinous processes (easy to palpate; interspaces widen in flexion for lumbar puncture)
  • Articular facets oriented roughly sagittally, allowing flexion and extension but little rotation
  • Mammillary and accessory processes (muscle attachments)
  • Pars interarticularis: the bone between the superior and inferior articular processes, the site of stress fractures
  • Triangular vertebral foramen containing the conus medullaris (L1) and cauda equina
Relations

Lumbar nerve roots exit below the pedicle of the same-numbered vertebra (L4 exits through the L4–L5 foramen). The psoas major arises from the sides of the bodies; the abdominal aorta and inferior vena cava lie anteriorly.

Mentioned in

Generated automatically from links in other entries.

Lumbar disc herniation and nerve rootsPosterior view of L4, L5 and S1. Each lumbar root exits below the pedicle of its own vertebra. A posterolateral herniation of the L4–L5 disc compresses the traversing L5 root; a far-lateral herniation at the same level compresses the exiting L4 root.L4L5S1L4–L5 discL5–S1 discDural sac / cauda equinaL4 rootL5 rootS1 root② far-lateral → L4① posterolateral→ L5 (traversing)RootWeaknessReflexSensory lossL4Knee extension, ankle dorsiflexionPatellar ↓Medial leg / ankleL5Great-toe extension, hip abductionNone reliableDorsum of foot, 1st webS1Plantarflexion, eversionAchilles ↓Lateral foot, sole

Swipe sideways to see the whole diagram →

Lumbar disc herniation and nerve roots. Posterior view of L4–S1 (right-sided roots shown). Lumbar roots exit below their own pedicle, so a posterolateral L4–L5 herniation (1) compresses the traversing L5 root and a far-lateral herniation (2) compresses the exiting L4 root.
Original schematic, created for this atlas.
Lumbar puncture anatomy (sagittal view)The spinal cord ends at the conus medullaris at about L1–L2; the cauda equina continues in the dural sac, which ends at about S2. A needle entering between the L3 and L4 spinous processes passes the ligaments and epidural space into the subarachnoid space below the cord. The intercristal line crosses L4.T12L1L2L3L4L5SacrumSpinal cordConus medullaris (L1–L2)← Cauda equinaDural sac ends ≈ S2Supraspinous / interspinous lig.Ligamentum flavumEpidural space → dura → CSFLP needle (L3–L4)Intercristal (Tuffier) line ≈ L4AnteriorPosterior

Swipe sideways to see the whole diagram →

Lumbar puncture anatomy. Sagittal schematic (not to scale): the cord ends at about L1–L2, the dural sac at about S2. The needle enters at L3–L4, just above the intercristal line (≈ L4), well below the conus.
Original schematic, created for this atlas.
Lumbar vertebra from above and behind showing the large kidney-shaped body, superior and inferior articular processes, mamillary and accessory processes
Lumbar vertebra from above and behind: massive body, mamillary and accessory processes.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 93. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Spondylolysis PANCE

Mechanism / lesion

Stress fracture of the pars interarticularis, most often at L5, from repetitive hyperextension in adolescent athletes (gymnastics, football linemen, diving, dance).

Classic presentation

Low back pain in an adolescent athlete, worse with extension. Positive single-leg hyperextension (stork) test. On oblique X-ray, a "collar" on the "Scottie dog".

Spondylolisthesis PANCE

Mechanism / lesion

Forward slip of one vertebra on the one below. Isthmic (from bilateral spondylolysis, typically L5 on S1) in younger patients; degenerative (facet arthropathy, typically L4 on L5) in older adults, especially women.

Classic presentation

Low back pain, hamstring tightness, radicular symptoms, and a palpable step-off of the spinous processes. Graded by percentage of slip on a lateral X-ray.

Lumbar spinal stenosis PANCE

Mechanism / lesion

Narrowing of the central canal, lateral recesses or foramina from disc bulging, facet hypertrophy and ligamentum flavum thickening, usually in adults over 50.

Classic presentation

Neurogenic claudication: buttock and leg pain, numbness or weakness on walking and standing (extension), relieved by sitting or bending forward (the "shopping cart sign": leaning on a cart helps). Pedal pulses are normal (unlike vascular claudication).

High-yield PANCE pearls

  • Adolescent athlete + back pain with extension → spondylolysis (L5 pars); Scottie dog collar.
  • Spondylolisthesis: step-off; isthmic L5–S1 (young), degenerative L4–L5 (older).
  • Spinal stenosis: pain with walking/standing, relief with flexion/sitting; MRI; normal pulses.
  • Lumbar roots exit below their same-numbered pedicle.

Imaging anatomy

X-ray

Lateral view grades spondylolisthesis; oblique views show the pars (the "Scottie dog": its neck is the pars, so a lucent "collar" indicates spondylolysis). Flexion–extension views show instability. X-rays aren't needed for acute nonspecific low back pain without red flags.

CT

Best to confirm pars fractures and assess healing.

MRI

First choice for spinal stenosis and radiculopathy (canal and foraminal narrowing, nerve root compression); STIR shows early pars stress reaction.

Key views & landmarks
  • Standing lateral lumbar radiograph (spondylolisthesis)
  • MRI lumbar spine (stenosis, radiculopathy with red flags or persistent symptoms)

Physical exam

Surface landmarks

The iliac crests mark about L4; the L5 spinous process lies just above the sacrum.

Palpation

Step-off between spinous processes (spondylolisthesis); paraspinal tenderness.

Strength / function testing

Lumbar range of motion (pain with extension suggests posterior element pathology; with flexion, disc). Lower limb neurologic exam and pulses (neurogenic vs vascular claudication).

Single-leg hyperextension (stork) test

Technique

The patient stands on one leg and extends the lumbar spine (± rotation toward the stance side).

Positive test

Reproduction of low back pain on the stance side.

Significance

Suggests spondylolysis (pars stress injury), though it isn't specific.

Self-quiz

Q1.

A 15-year-old gymnast has 2 months of low back pain that worsens with back walkovers and standing on one leg while arching her back. What is the most likely diagnosis?

Show answer

B

Spondylolysis (a pars interarticularis stress fracture, usually L5) is typical in adolescents doing repetitive hyperextension. The stork test reproduces the pain.

Q2.

A 72-year-old man has buttock and leg pain after walking two blocks that improves when he sits or leans forward on a shopping cart. Pedal pulses are normal. What is the most likely diagnosis?

Show answer

B

Neurogenic claudication relieved by flexion (sitting, leaning forward) with normal pulses is classic for lumbar spinal stenosis. Vascular claudication is relieved by standing still and has reduced pulses.

Q3.

On an oblique lumbar radiograph, a lucent defect across the "neck of the Scottie dog" represents a defect in which structure?

Show answer

C

The Scottie dog's neck is the pars interarticularis; a lucent "collar" indicates spondylolysis.

Q4.

A 68-year-old woman has back pain and neurogenic claudication. Lateral radiographs show a degenerative spondylolisthesis. At which level is this most typical?

Show answer

C

Degenerative spondylolisthesis (from facet arthropathy) typically occurs at L4 on L5 in older adults, especially women. Isthmic spondylolisthesis (from bilateral spondylolysis) typically occurs at L5 on S1 in younger patients.

Q5.

The roughly sagittal orientation of the lumbar facet joints allows which movements?

Show answer

A

Lumbar facets are oriented roughly sagittally, allowing flexion and extension but little rotation. Thoracic facets lie roughly in the coronal plane, favoring rotation (limited by the ribs).

Flashcards

See also